1. Field of the Invention
The present invention relates to an exhaust emission control system in an internal combustion engine comprising a spark plug disposed to face a combustion chamber, an intake system in which a fuel injection valve is disposed, an exhaust system having a catalytic converter incorporated therein and filled with a catalyst for reducing nitrogen oxide (NO.sub.x) in the presence of hydrocarbons in an oxidizing atmosphere, and an exhaust gas circulation amount control means capable of measuring and controlling the amount of exhaust gas circulated from the exhaust system to the intake system.
2. Description of the Prior Art
Such an exhaust emission control system has been conventionally known, for example, from Japanese Patent Application Laid-Open No. 156142/91.
In the above prior art system, the concentration of hydrocarbons in an exhaust gas is increased in order to increase the elimination rate of NO.sub.x when the temperature of the catalyst is high. However, in order to sufficiently increase the elimination rate of NO.sub.x by the catalyst for reducing the NO.sub.x in the presence of hydrocarbons in an oxidizing atmosphere, a control taking the concentration and type of hydrocarbons and temperature of the catalyst into consideration is required.